1. Field of the Invention
The present invention relates to an ultrasonic signal processor operated at multiple frequencies by means of using an input interdigital transducer (IDT) with a dispersive type of electrode-finger pattern and an output IDT with a dispersive-slant type of electrode-finger pattern.
2. Description of the Prior Art
Conventional ultrasonic transducers for signal processing such as a wedge-shaped transducer and a piezoelectric thin film transducer make use of disappearing of an output electric signal, which disappears in response to a disappearance of an ultrasound on a panel plate by touching thereon. In addition, it is difficult for conventional ultrasonic transducers to be operated under multiple frequencies. Disappearing of the output electric signal makes signal analysis complicated, and makes it difficult for the conventional ultrasonic transducers to be of use as hardware for the coding technique, when assembled in personal computer (PC) such as wearable PC, desktop- and laptop PCs, and notebook PC.
Conventional hardware such as magnetic cards and IC cards make it difficult to keep the information secret. The magnetic cards are very convenient and popular, however it is easy to make copies thereof or steal passwords. The IC cards are superior to the magnetic cards in difficulty in counterfeiting of cards, however it is not enough to keep the information secret thoroughly. In order to keep the information through PC secret, and to prevent the influence of noises and invaders, and then to keep a communication secret, it is necessary to construct a security system for PC.
An object of the present invention is to provide an ultrasonic signal processor operated at multiple frequencies capable of transmitting an ultrasound on a nonpiezoelectric plate.
Another object of the present invention is to provide an ultrasonic signal processor operated at multiple frequencies capable of sensing a touch position on the nonpiezoelectric plate from an appearance of an electric signal, which appears in response to the disappearance of the ultrasound on the nonpiezoelectric plate by touching thereon.
Another object of the present invention is to provide an ultrasonic signal processor operated at multiple frequencies capable of accurate sensing of a minute touch position on the nonpiezoelectric plate with a high sensitivity, high resolution, and a quick response time.
Another object of the present invention is to provide an ultrasonic signal processor operated at multiple frequencies making a contribution to the coding technique.
Another object of the present invention is to provide an ultrasonic signal processor operated at multiple frequencies preventing the influence of noises and invaders.
Another object of the present invention is to provide an ultrasonic signal processor operated at multiple frequencies making it difficult to steal information.
Another object of the present invention is to provide an ultrasonic signal processor operated at multiple frequencies keeping a communication secret.
Another object of the present invention is to provide an ultrasonic signal processor operated at multiple frequencies excellent in manufacturing and mass production.
Another object of the present invention is to provide an ultrasonic signal processor operated at multiple frequencies capable of operation under low electric power consumption with low voltage.
A still other object of the present invention is to provide an ultrasonic signal processor operated at multiple frequencies having a small-sized circuit with a simple structure which is very light in weight.
According to one aspect of the present invention there is provided an ultrasonic signal processor operated at multiple frequencies comprising a nonpiezoelectric plate, an input IDT, an output IDT, a first piezoelectric substrate, and a second piezoelectric substrate. The input IDT with a dispersive type of electrode-finger pattern has an overlap length L and interdigital periodicities Pi (i=1, 2, . . . , m). The output IDT with a dispersive-slant type of electrode-finger pattern has the electrode-finger direction slanting to that of the input IDT by an angle xcex8, and also has an overlap length LP along the electrode-finger direction of the output IDT and interdigital periodicities Qi (i=1, 2, . . . , m) along the orthogonal direction to the electrode-finger direction of the output IDT. The input- and output IDTs, and the first- and second piezoelectric substrates form a transducer-unit.
If one of input electric signals Si (i=1, 2, . . . , m) with frequencies fi (i=1, 2, . . . , m) corresponding to the interdigital periodicities Pi, respectively, is applied to the input IDT, a SAW is excited in the first piezoelectric substrate. The SAW is transmitted to the second piezoelectric substrate along an upper end surface of the nonpiezoelectric plate. And then, the SAW is transduced at the output IDT to electric signals Ej (j=1, 2, . . . , n), of which the phase delays linearly correlate to SAW propagation lanes Wj (j=1, 2, . . . , n) between the input- and output IDTs on the upper end surface of the nonpiezoelectric plate.
According to another aspect of the present invention there is provided an output IDT having the interdigital periodicities Qi and the overlap length LP. Each of the interdigital periodicities Qi is equal to the product of the corresponding one of the interdigital periodicities Pi and cos xcex8. The overlap length LP is equal to the product of the overlap length L and sec xcex8.
According to another aspect of the present invention there is provided an ultrasonic signal processor operated at multiple frequencies further comprising a third piezoelectric substrate, a coding IDT, a terminal IDT having the electrode-finger direction parallel to that of the coding IDT, a fourth piezoelectric substrate, an initial IDT, a decoding IDT, and a signal analyzer. The coding IDT consists of electrode-finger pairs, of which two neighbors are at a distance from each other, and has a coded pattern. The distance equals one of the interdigital periodicities Pi. The decoding IDT has the same construction pattern as the coding IDT. In the ultrasonic signal processor operated at multiple frequencies, if touching one of the SAW propagation lanes Wj, one of the electric signals Ej is detected at the output IDT, and then, it arrives at the coding IDT. In this time, a SAW based on the coded pattern is excited on the third piezoelectric substrate. The SAW based on the coded pattern is detected as a coded burst-signal at the terminal IDT. The coded burst signal arrives at the initial IDT, so that a SAW is excited on the fourth piezoelectric substrate. In this time, if the SAW on the fourth piezoelectric substrate correlates to the coded pattern, a pulse is detected at the decoding IDT. The pulse arrives at the signal analyzer. As a result, the touch position, that is, the one of the SAW propagation lanes Wj is sensed by means of the phase of the pulse.
According to another aspect of the present invention there are provided first- and second piezoelectric substrates made of a piezoelectric ceramic, respectively, the polarization axis thereof being parallel to the thickness direction thereof.
According to another aspect of the present invention there are provided first- and second piezoelectric substrates having a thickness smaller than the smallest one of the interdigital periodicities Pi, and a nonpiezoelectric plate having a thickness larger than three times the largest one of the interdigital periodicities Pi.
According to another aspect of the present invention there is provided an ultrasonic signal processor operated at multiple frequencies, wherein the phase velocity of the SAW on the nonpiezoelectric plate alone is higher than that in the first- and second piezoelectric substrates alone.
According to other aspect of the present invention there is provided an ultrasonic signal processor operated at multiple frequencies comprising the nonpiezoelectric plate and two transducer-units, of which each consists of at least one input IDT, at least one output IDT, the first piezoelectric substrate, and the second piezoelectric substrate. If one of the input electric signals Si is applied to the input IDT, a SAW is excited in the first piezoelectric substrate. The SAW is transmitted to the second piezoelectric substrate along the upper end surface of the nonpiezoelectric plate, and then it is transduced to the electric signals Ej at the output IDT.
According to a further aspect of the present invention there is provided an ultrasonic signal processor operated at multiple frequencies comprising the nonpiezoelectric plate, two ultrasonic units, the third piezoelectric substrate, the fourth piezoelectric substrate, and the signal analyzer. Each of the ultrasonic units consists of the input IDT, the output IDT, the first piezoelectric substrate, the second piezoelectric substrate, the coding IDT, the terminal IDT, the initial IDT, and the decoding IDT.